Growing plant life, such as food crops, tobacco, decorative flowers, ferns and the like can be damaged by exposure to excessive amounts of sunlight, extremes of temperature, rain, strong wind and other natural hazards. With ferns, especially, it is a universal practice to grow the plants under shelters, because strong sunlight will turn the leaves from a desirable green to an undesirable yellow in a matter of just a few days. While the present invention is to be described with particular reference to protecting growing ferns from exposure to excess sunlight, it is to be understood that it protects and benefits plant life in general from exposure to all of the hazards broadly mentioned above. Moreover, the invention is useful wherever shade structures are desirable, such as animal protecting covers, recreation area covers, swimming pool covers, patio covers, marina covers, automobile covers, industrial storage area covers, and the like.
The growing of ferns for commercial purposes was begun in certain areas of the southern United States where natural shade was available under tall, lacy branched and lightly-leaved trees. This produced the desired dappled sunlight effect, but the practice had two major disadvantages: (i) the increasing demand for fern-foliage soon used up the land available under the trees, and (ii) the use of fertilizers on the ferns also stimulated the trees to produce heavier leafing, which increased the shade density to the point where fern growth was retarded. The practice then became established of constructing wooden post and beam structures, covered with chicken wire and overlaid with rosemary bushes. These structures, while still in use, were expensive to construct because the wooden posts and beams required 10 .times. 12 foot centers for strength, the rosemary bushes were relatively heavy and much labor was required to maintain them. More recently, shade-producing fabric, and especially shade-producing plastic fabric strips have become available and the shade producing structures are being modified to the extent that the chicken wire and rosemary bush construction is being supplemented by a combination of wires stapled into a network on the upright posts and then the plastic fabric is fastened to each wire. These constructions, however, are all based on prior practices, and suffer many disadvantages in common. For example, the 10 .times. 12 foot centers on the uprights require 378 expensive posts per acre, the wires flex and break, the wires cut the fabric, and, because of the relatively close spacing of the uprights, labor saving tractors cannot go down the rows of plants to apply fertilizers, herbicides, and the like.
In all cases, a most serious problem with such prior art structures for protecting plants is their susceptibility to damage by wind. This is very expensive for three reasons: (i) the labor to reconstruct the structure is great, (ii) the cost of replacing the materials is considerable (plastic cloth at the present time costs about $3000 per acre); and (iii) the exposure of tender plants to the hot sun for more than a short time can cause irreversible damage to them.
Many proposals have been advanced for constructing shade producing structures capable of covering large tracts of land while still retaining a degree of resistance to destruction by wind. All of the prior art structures, however, have one or more serious shortcomings. In Hayes, U.S. Pat. No. 727,541, a structure is shown in which transverse wires are supported on posts and strips of the shade-producing fabric are woven longitudinally through the wires. The primary shortcomings in such a design reside in the lack of a means to prevent the cover from billowing, the fact that the cloth cannot be removed fast to avoid damage if a hurricane should come through; and the alternating arrangement of wires, top and bottom of the cloth, can cause the uprights to loosen and lift out of the ground. Womelsdorf, U.S. Pat. No. 2,974,442, shows shade cloth pinned to support wires. Since the wires are fastened to the uprights, the wind will tend to blow the posts out of the ground, as the shade cloth billows; and each pin would have to be pulled to unfasten the cloth for safe-keeping in the event of an approaching storm. Allen, U.S. Pat. No. 3,140,563, discloses a large cover on posts and cables, which can be retracted in the event of an approaching storm. However, there is no means of tying down the cover to prevent excessive billowing and the retracting mechanisms are complex and subject to jamming. Putnam, et al., U.S. Pat. No. 711,225, discloses a post and beam construction with longitudinal wire supports for covers which roll like window shades into aboveground containers. This structure has no means for holding down excessive billowing, and the structure cannot be dissembled quickly in the event of an approaching storm.
A new structure has now been developed which overcomes all of the above-mentioned disadvantages in a novel way. An essential holddown feature keeps the cover fixed to the ground when the wind blows, but still enables the cover to be easily and quickly removed when high force winds, such as hurricane strength storms, are expected. After the storm has abated, the shade-producing cover can be readily and quickly replaced, before the plant life is destroyed or damaged by exposure to the sun, and the like.